What are the complete set of combat modifers for fighting in darkness?

Question

I am slightly confused on combat in darkness. There are modifiers for blinded combatants and invisible combatants, but not specifically combatants who cannot see due to darkness. Are they all considered blinded? Are they blinded AND their opponents are invisible? What are the attack (melee or ranged) and AC modifiers for each combatant in the scenarios below, assuming the combat area is completely dark (due to no light source in a cave, magical darkness, etc.)?

1. Neither adversary can see in the dark.
2. Only one of the adversaries can see in the dark.

Answer 1

The defender has a -2 to defenses and loses his Dexterity bonus to AC (for being effectively blinded by total darkness), but the attacker has a crippling 50% miss chance because his target is in total darkness (concealment).

The only remaining thing to decide, then, is whether the attacker gets the +2 to attack rolls granted by invisibility. Note that invisibility also prevents opponents from gaining Dex to AC, but this is already covered by the Blind condition).

Personally, I would rule against giving the attacker the +2 to hit. Invisibility is, in my opinion, attempting to mimic the effects of being blind to a single target (that is, the attacker doesn't have +2 to hit, the defender has -2 to AC versus the attacker, but this is easier tracked as a bonus to the attacker's roll than a penalty to the defender's AC). Note that the defender's AC is already drastically decreased by the darkness, and the attacker's main issue in many cases is going to be beating the concealment miss chance, so whichever way you rule on this shouldn't matter too much.